A user's mobile device can't connect to Microsoft Exchange Online in Microsoft Office 365 through Microsoft Exchange ActiveSync. However, the mobile device previously could connect.
This issue can occur for many reasons. These include, but aren't limited to, the following:
- The device can't connect to the Internet service provider (ISP) or to the Internet.
- The device isn't set up correctly.
- The Exchange Online mailbox server that supports the connection isn't available because of maintenance or an outage issue.